Rotary cutter



Dec., 21, E948. l c. c. RUTBELL, l 294561842 A ROTARY CUTTER Filed Oct.13, 1943 v Patented Dec. 2l, 1948 ROTARY CUTTER Clarence C. Rutbell,Endicott, N. Y., assigner to International Business MachinesCorporation, New York, N. Y., a corporation of New York ApplicationOctober 13, 1943, Serial No. 506,073

Claims. (Cl. 29-105) This invention relates generally to an improvedform of fly cutter and more particularly to a tool for cutting the teethof a rack.

An object of the invention is the provision of a rack cutter havingcutting teeth spaced more accurately and proportioned more truly thanthose of the prior art. This end is achieved by the use of a threadgrinding machine to form the teeth of the cutter.' Although the teethare cut as portions of a helical thread, the extending helix edge doesnot interfere with cutting operations because the teeth are backed offand' relief is provided by grinding the teeth from a center which iseccentric relative to the center of cutting operation. Such eccentricbacking of! does not change the shape of the cutting teeth at any givenplane of cross section, with the result that successive sharpenings donot change the effective shape of the cutter teeth.

Another object of the invention is the provision of improved means forfastening a ily cutter tool bit in a holder.

A feature of the invention is the forming of multiple y cutter teeth assuccessive parts of a helical thread.

A further object ofthe invention is the provision of back-off or reliefIclearance for helical cutting teeth.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose. by Way of example, the principle of the 1 invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. l is a side elevation view of the rack cutter.

Fig. 2 is an end view of the cutter of Fig. l.

Fig. 3 is a detail view showing the shape o! the cutting teeth ascooperating with a work piece.

Fig. 4 is a detail view of an alternative tooth Fig. 5 is an .end viewof a cutter with a tool bit of an alternative form and having suitablesecuring means.

Fig. 6 is a diagrammatic view of a cutting tooth showing therelationship oi' actual tooth outline with respect to normal and helicaltooth outlines and the effect of eccentric formation for backing ofi?.

In Figs. 1 and 2 it is seen that a tool holder body or frame is formedwith a circular shaft or arbor opening 2i and a keyway 22. In the holderis ground or cut a rectangular groove -to receive a tool bit or cutterbar 23, extending longitudinally -along the holder. Along one wall ofthe bit is cut a' sloping groove 24 which is at right angles to a seriesof tapped holes vcontaining screws 26 for securing the blt in theholder.

At the top of the projecting part of bit 23 is formed a series of rackcuttingteeth 21 which are required to be accurately proportioned andvery evenly and equally spaced. In forming these teeth, they are not cutin the conventional manner or shaped as plain rack cutting teeth.Instead, the tool with bar 23 as a blank is put in a thread grindingmachine and teeth 21 are ground as parts or portions of what would be acomplete helical thread around body 20, if the body extended to theouter edge of the bit.' However, since teeth 21 are part of a helicalthread, they lean to the side (Fig. 1) and have edges not confined toplanes at right angles to the axis A of the holder. Therefore, in orderto provide clearance for cutting operation, the teeth are ground to bebacked off to form relief angles diverging away from the cutting edgesand the cut material. As shown in Fig. 2, the center used for cuttingthe teeth as helical portions is not the axis A but the eccentriclcenter E. This center E is not only eccentric with respect to A. but itis also removed from the plane at right angles to the plane includingaxis A and the cutting face of the teeth. In other words, in Fig.y 2 thetooth 21 is seen to slope down to the right because it is generated fromcenter E which is eccentrlcally and angulaily disposed relative tocenter "A. Both sides of the teeth also have cutting clearances insteadof an opposing angle that one side of a helix would ordinarily have.

It is understood that the teeth are not necessarily ground while the bitis mounted in the holder 20. Special eccentric arbors and backingoifholders are used if the relief angle is so steep as to causeinterference between the grinder and a holder of cylindrical shape.

The diagrammatic showing in Fig. 6 shows the diierence between a normaltooth, a helical tooth and a backed-off or eccentrlcally ground helicaltooth. The tooth 21 of the invention is shown in full lines with thecutting edges at the right. A line is pointed out as a normal toothline, i. e., a radial line from the cutting corner. Such a line lies ina plane at right anglesto the axis. Angularly disposed to the lirst lineis the helical tooth line as it would be if not backed oil. This angleis a measure of interference with cutting when the bit is arrangedparallel with the axis of the holder but could be useful at the properangle 4tions back of the initial cutting face;

3 on the holder. However, by merely forming the helical portioneccentrically, proper relief angles or back-off is provided in alldirections asnoted by comparison of the full lines with those inphantom.

As an actual example, a tooth may be taken in a thread with a pitch of,A.1309 and a circumference of about 13 inches. This calls for a helixangle of about 35. Since' the teeth have an angle of 141/2" on a side,and the tangent of 141/2 being .258, it is necessary to back olf thetooth approximately four times 0 35' to overcome the helix angle. Inaddition to this, it is necessary to back off about 4 for every yactual1 of clearance desired. Therefore, if there is a total of 9 of radialrelief or back-oma tooth has 9 clearance on top, 9/4-0 35'=1 40 on oneside, and 9/4-l-0" 35=2 50' on the other side. The tooth form is correctdespite these different clearances and cutting is performedsatisfactorily.

The shape of the tooth is constant for all sec- Since the tops of theteeth are ground in the same threading set-up, the result is a cutterthat may be sharpened many times and still retain the same form.

In Figs. 3 and 4 the teeth 21 and 21' are shown as they cooperate withthe work W to be cut. 'I'he long tooth 21 (Fig. 4) cooperates with apiece having a nished surface and requires no cutting by the root edgesof the cutter teeth. Although both types of cutting teeth shown are ofthe Acme style, it is apparent that the advantages of the presentinvention are realized as well with other tooth forms.

In Fig. is shown an alternative mode of securing the tool bar or bit23'. There it is seen that the tool body or cylinder 20 not only isformed Ywith a rectangular groove for receiving the bit, but alongsidethe groove is a at area 30 which coincides with a shoulder 3| on theside of bit 23'. Extending inward perpendicular to flat 30 is a seriesof tapped holes 32 for receiving screws, the heads 33 of which overlapthe groove wall and press down ori shoulder 3| to hold the bit on thecylinder.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a singlemodiflcation, it will be understood that various omissions andsubstitutions and changes in the lform and details of the deviceillustrated and in its operation may be made by those skilled in the artwithout departing from the spirit of the invention. It

is the intention therefore to be limited only as indicated by the scopeof the following claims.

What is claimed is:

1. In a y cutter, a cylindrical tool body with a cutting tooth, saidtooth formed as a portion of a helical thread, the axis of generation ofsaid helical thread being eccentric with respect to the axis of saidtool body to back off the tooth surfaces enough to provide relief angleson all sides.

2. In a ily cutter, a cylindrical tool frame with a plurality of spa-cedand axially aligned rack cutting teeth, said teeth formed as parts of athread which if completed would be a continuous helical thread, the axisof generation of said thread being eccentric with respect to the axis ofsaid frame, said eccentricity being suicient to back off the toothsurfaces more than the 'intervference of the helix angle.

3. In a. ny cutter, a cylindrical tool body formed with an outer axialgroove, a rectangular tool bit tted in said groove,fmeans for securingsaid bit to said` tool body. said bit being formed with a series ofregularly spaced cutting teeth, each tooth being a portion of a helicalthread. the surfaces of each tooth being backedy off and gener. atedfrom a center which is eccentric with respect to the axis of thecylindrical tool body whereby the tooth surfaces are backed off toprovide a relief angle and more than compensate for the iny terferenceof the helix angle. i

y 4. In a multiple toothed rack cutter, a cylindrical tool holder formedwith an inner .axial opening and keyway and an outer rectangular grooveextending axially, a rectangular tool bit center of said holder wherebyIthe parts of the teeth behind the cutting edge are backed/oil' for endand side relief to overcome the interference of the helix angle.

5. As an article of manufacture, a rack cutter having a plurality ofteeth which are portions of a helical thread, said teeth being backedoff eccentrically to provide enough clearanceto compensate for theinterference of the helix angle.

6. As an article of manufacture, a multiple toothed fly cuttercomprising a cylindrical portion and an outer axial cutting rib, saidrib being formed with teeth each of which is a portion of a helicalthread, said teeth being backed off for clearance sufficiently tocompensate for the interference of the helix angle and provide a reliefangle.

7. In a cutter, acylindrical tool body with a cutting tooth of slopingsides, said tooth being formed as a portion of a helical thread, theaxis of generation of said helical thread being eccentric with respectto the axis of said tool body to provide a back ofi` clearance angle,the resulting side clearance angle overcoming the helix interferenceangle being found by the following formula:

Resulting side tangent of clearance angle tooth slop'e X in degreesangle given back offy angles in P6115; angle degrees 1H egrees axis ofgeneration of said thread being eccentricl With respect to said frame toprovide a top tooth clearance angle and a, side clearance angle, therequired top angle to overcome the interference of the helix angle beingfound by the following equation:

Required=desired side clearance angle-lehelx angle top angle tangent oftooth slope angle 9. As an article of manufacture, a rack cutter havingat least one cutting tooth which is a portion of a helical thread, saidtooth having sloping sides and being backed oi at an angle to provideaside clearance angle to more than compensate for the interference of thehelix angle, said back oil! clearance angie being found by the followingformula:

Needed back specified side clearance +helix angle off angle angle indegrees in degrees 111 egress tangent of tooth slope angle Distance ofoutside, eccentricity diameter X of thread clearance angle tangent 258CLARENCE C. RUTBEIL.

angle Desired side helix) REFERENCES CITED The following. references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date Brown Nov. 29, 1864 Muller Aug.3, 1920 Stauder Nov. 16, 1920 Kearney Oct. 14, 1930 Walker Har. 15, 1932Irwin A555. 30, 1932 -Aclrley May 11, 1937 Kruse Feb. 17, 1942 WildhaberMar. 30. 1943

